It didn't take long for the world to figure out the combat
potential of airplanes.
In 1911, only eight years after the Wright brothers got their
creation off the ground, the U.S. military started dropping
test bombs from airplanes. A few years later, World War I
troops were battling it out in the sky with
machine-gun-packing fighter planes.
moved pretty quickly from there. Only 60 years later, the
early single-engine propeller planes had evolved into sleek,
powerful fighter jets that could make sharp aerial turns at
more than 600 miles per hour (970 kph).
In this edition of HowStuffWorks,
we'll look at one of the most famous fighters, the F-15. This
remarkable aircraft is getting up in years -- it has been
around since the early '70s -- but it's still a crucial piece
of the U.S. arsenal. According to the U.S. Air Force, it has a
perfect combat record, with over 100 victories and zero
defeats. As we'll see, its success is due to its phenomenal
maneuverability, advanced electronic equipment and fearsome
What is an F-15?
The F-15 Eagle is a
small, highly maneuverable jet plane designed to fly combat
missions in all weather conditions. Its primary mission is
maintaining air superiority. In other words, its
ultimate purpose is to defeat other planes in aerial combat.
The United States Air Force commissioned the plane after
they got a look at the MiG-25, a powerful fighter jet the
Soviet Union unveiled in 1967. The MiG-25, commonly known as
"the Foxbat," was far superior to the primary U.S. fighter jet
at the time, the F-4 Phantom, and in the heart of the Cold
War, the Air Force needed a comparable aircraft as soon as
possible. McDonnell Douglas (now merged with Boeing) won the
contract for the new project and delivered the finished F-15 a
few years later. The company has introduced several variations
on this plane since then, as technology and needs have changed
(see below). The current combat F-15 Eagle is the
The original F-15 Eagle was designed to handle only
air-to-air targets (other planes). It wasn't built to bomb
targets on the ground because the Air Force knew that the
extra equipment would compromise the plane's aerial combat
abilities. But when the Air Force needed a fighter bomber to
replace the aging F-111 until the new stealth F-117
was ready, they decided to modify the F-15 for air-to-ground
missions. The result was the F-15 Strike Eagle, designated
The Strike Eagle is not a replacement for the original
F-15, but a supplementary bomber plane. Surprisingly, the Air
Force's temporary solution turned out to be one of the best
fighter bombers ever made. In Operation Desert Storm, the
Strike Eagle proved it could successfully fight its way past
enemy planes, hit several ground targets, and then fight its
way out of enemy territory.
In the next section, we'll see how these two planes are put
together and find out how they dive, climb and dodge so
- F-15A - The original F-15 combat plane, the
F-15A first flew in July 1972. Like the current F-15C,
this plane is designed for a single pilot.
- F-15B - The original F-15 training plane,
the F-15B first flew in July 1973. This plane has two
pilot stations -- one for an experienced instructor
and one for a pilot in training.
- F-15C - An updated version of the F-15A,
the Air Force added the F-15C in 1979. The F-15C has
improved electronics, greater engine power and
increased fuel capacity.
- F-15D - This is the two-seater
training-plane counterpart to the F-15C.
- F-15E - A combination air-to-air fighter
and air-to-ground bomber (also known as the F-15
Strike Eagle), the F-15E entered the Air Force arsenal
in 1988. The biggest difference between the F-15C and
the F-15E is the F-15E's extra cockpit station and its
bombing capabilities. There are many smaller changes
throughout the plane.
- F-15I Thunder - An Israeli variation on the
- F-15S - A Saudi variation on the F-15E
- F-15J Peace Eagle - A Japanese variation on
- F-15 ACTIVE - The F-15 ACTIVE is a
two-seater F-15 used in NASA research. ACTIVE stands
for "advanced control technology for integrated
vehicles." (Check out this
site for more information.)
Power and Flight
An F-15 has most of the
elements you'll find on an ordinary jet plane. It has two
wings that generate lift, it has rear vertical and
horizontal stabilizers and rudders that balance and steer the
plane, and it has twin turbofan jet
engines at the rear of the plane that generate thrust.
The main difference between an F-15 and an ordinary jet is
how these elements are balanced. The F-15's twin engines
(Pratt & Whitney F-100-PW-220s or 229s) have a very high
thrust-to-weight ratio, meaning they are relatively
light for the amount of thrust they generate (they can
generate almost eight times their own weight in thrust).
Photo courtesy Department
An Air Force
maintenance squadron tests out a Pratt Whitney
F100-PW-220e engine configured for the
The plane body is relatively light, too, though it is
extremely strong. The wing spars (the support structures
inside the wings) are made of titanium, which is lighter and
stronger than steel, and
most of the skin is made of lightweight aluminum. According to
the Air Force, each engine can generate between 25,000 and
29,000 pounds of thrust. The F-15C's normal weight is only
45,000 pounds, which means its thrust is actually greater than
its weight! This lets it accelerate quickly, even while
climbing in altitude.
The F-15 also has very low wing loading, meaning it
has a lot of wing area for its weight. Greater wing area means
greater lift, which makes the plane more agile. It can take
off, ascend and turn much more quickly than an ordinary plane,
which has much more weight per square foot of wing space.
Photo courtesy U.S.
An F-15's high
thrust-to-weight ratio and low wing loading let it shoot
off the ground at a sharp
The engines are outfitted with afterburner
nozzles, which can provide an extra kick of thrust when
necessary. The afterburner simply injects fuel into the hot
jet exhaust stream. It ignites, adding to the hot gases
shooting out the back of the engine (see this
Question of the Day for details on afterburners). At full
force, the plane can get up to more than Mach 2.5
(approximately 1,854 mph / 2,984 kph).
The high engine power does come at a price -- poor fuel
economy. Of course, the F-15 was designed with this limitation
in mind. In order to extend its un-refueled range, it was
built with large internal fuel tanks in the fuselage (the main
body) and in the wings. It can also carry three external
tanks, as well as a pair of aerodynamic form-fitting tanks
under the wings that generate some lift of their own. Fully
fueled, the F-15C can fly 3,450 miles (5,550 km), and the
F-15E can fly 2,400 miles (3,860 km).
Photo courtesy U.S.
The F-15 can
carry extra fuel in three external tanks. One mounts
under each wing and one attaches to the
The other problem with the engines is that they wear out
pretty quickly. This is to be expected, given the amount of
work they do. Fortunately, they're very easy to replace -- an
Air Force ground crew can do it in less than an hour!
The F-15 doesn't just take off quickly, it stops quickly
too. It has its own extendable air-brake, a
hydraulically operated panel that dramatically increases the
aircraft's drag to slow it down (just like a parachute).
The main thing that sets the
F-15 and other modern fighters apart from their predecessors
are their electronic systems. Early fighter pilots controlled
their planes mechanically, by moving linkages, and they mainly
used their own eyes to target enemy planes. In stark contrast,
nearly every aspect of the F-15 is computerized.
The plane is essentially a robot. It
has a central computer, which is connected to an array of
advanced sensors. Based on input from the inertial guidance
system (which contains highly sensitive gyroscopic
sensors) and the pilot, the computer activates hydraulic
actuators to adjust the wings and rear stabilizers. The pilot
doesn't actually fly the plane directly: He or she gives
instructions and the computer decides how to carry them out.
The computer is constantly making flight adjustments on its
own to improve flight performance -- the computer artificially
creates a relatively smooth ride. The F-15 computer can make
necessary adjustments in milliseconds, about a hundred times
faster than a human being.
main "eye" is its computer-controlled radar
system, mounted in the nose. The radar's job is to locate
other aircraft and generate ground maps. The dish is mounted
on moving gimbals, so it can pivot to scan different areas or
follow a moving target. The radar figures out which way
targets are moving using the pulse-Doppler system --
essentially, shifts in the reflected radio wave
frequency indicate whether the target is moving toward the
radar system or away from it (see How Radar
Works for more information.)
the Air Force, one F-15 Strike Eagle goes for $31.1
million. The F-15D is a relative steal at only $29.9
million, and a first generation plane will only cost you
$27.9 million. While this sounds like a lot to the
average person, it's actually a pretty good deal in the
military world. Airmen say it's a small price to pay for
the F-15's extraordinary performance
The F-15 Strike Eagle has additional scanning equipment
called the low-altitude
navigation and targeting infrared for night
(LANTIRN) system. The LANTIRN system is housed in two
pods mounted to the bottom of the plane, near the engine
The navigation pod holds another radar unit that is
optimized to map the ground terrain, and a forward-looking-infrared
(FLIR) night vision scanner that picks up the infrared
heat energy from surrounding objects. Together, these sensors
generate a detailed image of the ground below, allowing the
pilot or computer to fly in total darkness.
The targeting pod houses a powerful laser and
another FLIR scanner, mounted to a swiveling turret. The laser
works as a range-finder, calculating the distance to
targets based on how long it takes a laser beam to bounce off
of them, and also as a target designator, marking
targets for laser-guided
missiles. The targeting system is designed to pick out
ground targets, but it can also be used in air-to-air combat.
The central computer processes data from the radar and the
LANTIRN system and presents targeting and navigation
information to the crew. In the next section, we'll look
inside the cockpit to see how the crew accesses this
information, flies the plane and targets the enemy.
Inside the Cockpit
The original F-15 was
designed for a single-person crew. The pilot flies the plane
and targets enemy aircraft at the same time. The F-15 Strike
Eagle has an additional station in the back of the cockpit for
a weapons systems officer, or WSO (pronounced "wizzo").
In the Strike Eagle, the WSO is in charge of selecting and
eliminating ground targets while the pilot concentrates on
maneuvering the plane and fighting enemy aircraft. Both
stations are housed in a sturdy "bubble" canopy on top of the
plane. This canopy design gives the crew a full 360-degree
view of their surroundings.
Photo courtesy Department
bubble canopy gives the crew a wide view of the sky.
This plane is preparing to
The pilot's station is designed to make flying and
targeting as easy as possible. The computer presents most
relevant information on the heads-up display (HUD), a
monitor that projects an image onto a transparent screen at
the front of the cockpit canopy. With the heads-up display,
the pilot can monitor the flight data and the radar
information while keeping an eye on the sky. This is crucial
in combat -- a pilot can't keep looking down at gauges and
instruments while evading or chasing enemy fighters. The Air
Force is planning to eventually replace this system with a
helmet-mounted monitor that projects flight data onto the
The pilot's controls are also fairly straightforward. The
pilot steers the plane with a control stick located in
the center of the cockpit, and controls the engine with the
throttle on his or her left. Both controls have several
buttons and switches that operate the radar equipment, select
options on the heads-up display, and target and fire the
The controls are designed with the hands-on throttle and
stick (HOTAS) system. In the HOTAS system, every
switch and button on the controls has a different shape and
texture. This way, the pilot can control all the major aspects
of the plane without ever looking down into the cockpit.
Photo courtesy U.S.
Department of Defense
cockpit in the F-15 Strike Eagle (on the right) has an
extra station for the weapons systems
The WSO, by contrast, doesn't spend much time looking
outside the cockpit. He or she monitors radar, LANTIRN and
flight data on four multi-function displays (MFD) -- cathode ray
tube monitors surrounded by buttons (sort of like the
display on an automatic teller
machine). The WSO position has a full set of flight
controls, but this is only a back-up provision -- normally,
the WSO doesn't help fly the plane. Both the pilot and the WSO
sit in high-tech ACES II ejection
seats, which launch them clear of the plane in an
All of this expensive equipment serves one basic purpose:
It is designed to deliver various missiles, bombs and bullets,
known in military circles as ordnance, to enemy
targets. In the next section, we'll find out what the F-15 is
actually packing when it goes to war.
The F-15 Eagle is loaded up with
weaponry that can take out almost every aircraft in existence.
It sports eight air-to-air missiles of different designs. It
can carry various combinations of AIM-120
advanced medium range air-to-air missiles (AMRAAMs), AIM-9L/M
Sidewinder missiles, or AIM-7F/M
All three missile types are designed to actively seek out
their target. The AMRAAM and Sparrow missiles are both
radar-guided. The AMRAAM has its own radar unit and flight
control system. Before firing the missile, the F-15 computer
transmits radar information specifying the intended target,
and the missile's radar unit locks on. After the missile
launches, its one goal is to steer itself (by adjusting flight
fins) toward that target.
The Sparrow missile works on a similar principle, but it
doesn't have its own radar transmitter. The pilot has to keep
the plane's transmitter aimed at the target, to "paint" it for
The sidewinder missile uses an infrared sensor to pick up
on an enemy plane's hot engine exhaust. The flight controls
simply steer the missile toward the hottest area in sight.
The F-15 also has a built-in machine
gun, an M-61
20-mm 6-barrel cannon, mounted inside the starboard
(right) wing. The gun has an efficient Gatling
gun design that can fire about 6,000 rounds per minute. It
never gets the chance, however, because its magazine only
holds 940 rounds. It can empty its entire magazine in less
than 10 seconds!
The pilot selects a different targeting display on the HUD
for each weapon. The machine gun display, for example,
consists of a funnel shape. The pilot maneuvers the plane so
that the target is in the center of the funnel and then opens
The F-15 Strike Eagle has all of these weapons, and it can
also carry just about any air-to-ground missile in the Air
Force arsenal. It often carries guided munitions, such as the
bomb. All in all, it can carry approximately 23,000 pounds
(10,430 kg) of ordnance.
An F-15 Strike Eagle drops Mark 84
laser-guided bombs during a training
Both F-15 models also have a number of high-tech defenses.
They have radar warning receivers, which detect enemy radar
from ground stations, planes or guided missiles, and an
advanced radar jammer to confuse these radar units. They also
have a chaff dispenser, a device that shoots out a
cloud of metal strips. Enemy radar picks up the chaff and
temporarily loses its lock on the F-15.
The F-15's combination of high maneuverability,
sophisticated electronics and powerful weaponry have made it a
hugely successful weapon in the United States arsenal (and a
number of other countries' arsenals, as well). But now it's
approaching the end of its run. Boeing and Lockheed Martin
have already developed its replacement, the F-22
Photo courtesy U.S.
Raptor, the F-15's high-tech
The Raptor takes everything on the F-15 to a whole new
level, with much greater acceleration, maneuverability and
computer power. It's also designed for stealth flying,
just like the F-117 and B-2
bomber. When the F-22 enters service in 2005, the Air
Force will phase out the F-15 Eagle. The F-15 Strike Eagle
will keep flying for the foreseeable future.
For much more information about the F15, the F-22 and other
military aircraft, check out the links on the next page.
Lots More Information!
More Great Links